Add support for x86-xen_domu target

Config for rootfs and grub is not needed anymore (https://dev.openwrt.org/ticket/18074)

Config file not needed anymore (set implicitly by gluon now)

Avoid empty vars

targets/targets.mk

@@ -4,6 +4,7 @@ $(eval $(call GluonTarget,mpc85xx,generic))
 $(eval $(call GluonTarget,x86,generic))
 $(eval $(call GluonTarget,x86,kvm_guest))
 $(eval $(call GluonTarget,x86,64))
+$(eval $(call GluonTarget,x86,xen_domu))
 
 ifneq ($(BROKEN),)
 $(eval $(call GluonTarget,ramips,rt305x)) # BROKEN: No AP+IBSS support

targets/x86-xen_domu/profiles.mk

+$(eval $(call GluonProfile,GENERIC))
+$(eval $(call GluonProfileFactorySuffix,GENERIC,-ext4,.img.gz))
+$(eval $(call GluonProfileSysupgradeSuffix,GENERIC,-ext4,.img.gz))
+$(eval $(call GluonModel,GENERIC,combined,x86-xen))

targets/x86-xen_domu/vermagic

+bce85557e89d5a4f30d6d723503b1a61